1. Field of the Invention
The present invention relates to voltage regulators, and, more particularly, it relates to a voltage regulator which functions under normal operating conditions to control the charging of a battery by the regulation of the output voltage of a generator, and functions under a fault condition to regulate the output of a generator at a predetermined upper voltage limit.
2. Description of the Prior Art
Voltage regulators are used to control the charging or energization of a battery by the regulation of the output voltage of a generator. A common environment for a voltage regulator is in an automotive electrical system, where an automobile battery, which is nominally rated at 12 volts, is energized by a generator driven by the vehicle engine, which may assume a broad range of rotational speeds. The specific function of the voltage regulator is to maintain the battery voltage at a desired regulated level by the regulation of the generator output voltage, notwithstanding the rotational speed of the engine and the amount of load on the battery.
More specifically, the conventional generator includes a rotor having formed on it a field winding. The field winding is magnetically coupled to stator windings. The rotating magnetic field associated with the field winding induces AC voltages at the output terminals of the stator windings. These AC voltages are rectified into DC form and supplied to the battery through the cable interconnecting the generator and the battery. The regulation of the generator output most commonly takes place through the control of the energization of the field winding. The generator output is directly related to the current in the field winding, and by increasing or decreasing the field current, the generator output voltage may be increased or decreased accordingly.
It may occur that a fault or malfunction will interrupt the electrical connection between the generator output terminal and the battery, i.e. the battery cable between the generator output stud and the battery terminal may become defective and fail to pass current. In this instance, the battery will begin to discharge and relay to the voltage regulator a signal condition indicating that the battery needs charging. Accordingly, the voltage regulator will energize the generator field winding and increase the generator output voltage in an attempt to bring the battery up to the desired regulated voltage level. However, the interruption in the electrical connection between the generator and battery will prevent the battery from receiving the generator output voltage. The low battery signal condition that is supplied as input to the voltage regulator will persist, and tend to cause the generator to run away until it encounters a physical limitation on its output voltage level.
The voltage regulator should therefore be properly equipped with means for sensing the occurrence of an interruption between the output terminals of the voltage and the battery, and responding to the interruption by the regulation of the generator output voltage at an acceptable upper limit.
The prior art has addressed both the problems of voltage regulation under normal operating conditions, and voltage regulation under a fault condition. The patent to Harland, Jr. et al, U.S. Pat. No. 3,469,168 is exemplary of a voltage regulator circuit meeting these functional requirements. Specifically Harland, Jr. et al teaches a voltage regulator circuit for controlling the output voltage of a generator under normal operating conditions, and moreover for controlling the generator output voltage under a fault or malfunction condition.
However, the Harland, Jr. et al voltage regulator circuit is designed with a degree of complexity above the voltage regulator of the present invention. Design complexity is an important factor affecting product cost and reliability. When one contemplates the scale of production required to equip each automobile being manufactured with a voltage regulator circuit, it can be appreciated that design simplification represents a significant achievement in product reliability and cost reduction.
The specific point of complexity of the Harland, Jr. et al reference is the use of a Zener diode for the sensing element that senses the generator output voltage having reached a predetermined, upper limit. An objective of the present invention is to realize a simplification and improvement in the design of a voltage regulator circuit by replacement of the Zener diode with a less costly, more reliable sensing element.